: PRéCIS: Patients with CMS defined severe glaucoma often have clinically useful remaining RNFL, suggesting that structurally-based rather than functionally-based criteria would be more appropriate to use as guidelines for the utilization of OCT imaging. PURPOSE: RNFL OCT in glaucomatous eyes with advanced structural damage can reach a floor after which there is no further detectable thinning of RNFL. Insurers are considering limiting coverage for OCT in "severe stage glaucoma" defined by Centers for Medicare and Medicaid Services (CMS). However, CMS definitions of severe glaucoma are based primarily on visual field (VF) criteria. Many of these patients may have preserved RNFL in other sectors. This study aims to assess the clinical utility of RNFL measurements by OCT in eyes with CMS defined severe glaucoma. PATIENTS AND METHODS: Medical records of patients with CMS defined severe glaucoma were consecutively reviewed. Data collected included average/sectoral RNFL thickness, and VF mean deviation (MD). Previous estimates of RNFL floor and test-retest variability for Cirrus OCT were used to establish 3 threshold values of RNFL. Data analysis included descriptive statistics, chi-square analysis, and ANOVA. RESULTS: 129 eyes qualified (age: 71±12▒y; MD: -13.5±4.3▒dB; average RNFL: 60.9±7.9▒um), A majority (66%) of eyes met severe glaucoma criteria with defects in both hemifields; 34% met only paracentral defect criteria. The proportion of eyes that had significant remaining average, superior, or inferior RNFL, estimated by Thresholds 1-3, was 21-54%, 29-51%, and 16-37%, respectively. At least one vertical quadrant had significant remaining RNFL in 35-66% of eyes, depending on the threshold used. CONCLUSION: Our data demonstrate a substantial portion of eyes with CMS defined severe glaucoma have measurable RNFL above floor in at least one vertical quadrant that may be longitudinally monitored for progression. The presence of CMS defined severe glaucoma does not exclude the potential utility of OCT to monitor progression.